The power transmission device of this type is generally a power transmission device in which a wheel hub is rotatably disposed in an outer peripheral portion of an axle housing via a wheel bearing. A drive shaft is disposed in a central hole of the axle housing so as to be relatively rotatable to the axle housing. A gear speed reducer, which decelerates a rotation of the drive shaft and transmits the rotation to the wheel hub, is provided between the drive shaft and the wheel hub. In this power transmission device, the drive shaft is rotated by the driving of a driving source, such as an engine or an electric motor, causing the wheel hub to rotate via the gear speed reducer. As a result, a working vehicle can travel by a vehicle wheel attached to the wheel hub.
A brake chamber is provided between the axle housing and the wheel hub. The brake chamber is a space in which a wet multi-plate type brake mechanism, which is formed between the axle housing and the wheel hub, is housed. The brake mechanism applies braking to the rotation of the wheel hub relative to the axle housing when the brake mechanism is actuated. As a result, the traveling working vehicle can be decelerated.
In consideration of a cooling effect, wet-type friction plate and mating plate immersed in oil, serving as heat generation sources, are often applied as the brake mechanism (for example, see Patent Literature 1). In this related art, a floating seal is disposed between the brake chamber that houses the brake mechanism and a space including the wheel bearing in order to divide the two spaces. Meanwhile, a speed-reducer housing chamber that houses the gear speed reducer and the space including the wheel bearing are communicated with each other in order to lubricate the wheel bearing using oil stored in the speed-reducer housing chamber.